In general, a substrate processing apparatus for performing processes such as a film forming process on a substrate, e.g., a wafer, is used in a semiconductor device manufacturing process. As one example of the processes performed by the substrate processing apparatus, there is available a film forming process using an alternate supply method. In the film forming process using the alternate supply method, a film is formed on a processing target substrate by repeating a predetermined number of cycles (n cycles), each cycle including a precursor gas supply step, a purge step, a reaction gas supply step and a purge step for the processing target substrate. As one example of the substrate processing apparatus for performing the film forming process, there is available a substrate processing apparatus configured to supply various kinds of gases (a precursor gas, a reaction gas, a purge gas, etc.) onto a surface of the processing target substrate from an upper side thereof and to exhaust the various kinds of gases supplied onto the surface of the processing target substrate toward the upper side of the substrate.
The type of substrate processing apparatus includes a substrate mounting stand having a substrate mounting surface which supports a plurality of substrates along a circumferential direction, and a gas supply unit installed at a position to face the substrate mounting surface. The gas supply unit has a structure in which gases are alternately supplied with respect to the rotation direction of the substrate mounting stand. In the film forming process, films are formed on the substrates as the substrate mounting stand rotates at a lower side of the gas supply unit.
In case of rotating the substrate mounting stand having a plurality of substrates mounted thereon so that gases are alternately supplied onto the respective substrates, the respective gases are not mixed with one another and an amount of gases exposed onto the substrates is large, in terms of gas use efficiency or the like.
When gases are alternately supplied onto the substrates, the gases are also alternately supplied onto the surface of the substrate mounting stand which supports the substrates. Thus, a film is also formed on the substrate mounting stand. Since the film formed on the substrate mounting stand may adversely affect a film forming process, a cleaning process is periodically performed in the film forming apparatus. As one example of a cleaning method, a cleaning gas in a plasma state may be supplied into a process chamber.
However, in order to prevent the gases from being mixed or to allow the exposure amount of the gases to be large, as mentioned above, it is required to confine each of the gases within a specified space. The specified space may be, e.g., a space positioned below gas supply holes. If the cleaning gas is supplied in this structure, the cleaning gas is hardly diffused to spaces other than the specified space. Therefore, the cleaning process is performed unevenly on the substrate mounting stand. If the cleaning process is performed unevenly, over-etching by the cleaning gas may be incurred or a cleaning target is not sufficiently cleaned.